This invention relates to a device for controlling the quantity of zebra mussels entering submerged water intakes, and more particularly to a device utilizing both electrical current and air bubbles for such control.
Zebra mussels were first discovered in Canada in Lake St. Clair in 1988. They appear to have been transported to North America from Europe in the ballast of a ship in 1985 or 1986. The rapid colonization of these mussels in the Great Lakes and connecting rivers has raised issues of both environmental and economic importance. One particular concern is the blockage of water intake pipes. Zebra mussels adhere strongly to virtually any surface, and accumulate in multilayer colonies. The cost of controlling such mussels at water intake pipes in Canada and the United States could reach billions of dollars by the year 2000.
Water intakes pipes in North America were not designed to cope with zebra mussels, and the extent of the problem and its solutions may differ from the European experience. Many methods to control zebra mussels have been identified in the European literature, those methods being classified as physical, mechanical and chemical. The physical methods include heat, ultrasound, ultraviolet waves, and electricity. The chemical methods, which are in wide use in Europe, involve use of chlorine, ozone and other biocides and are now being used to control zebra mussels at water intakes in Canada and the United States. There are, however, many growing environmental and health concerns associated with use of chlorine and other biocides. Because of these concerns, chemical methods are considered temporary solutions. Also, chemical biocides cannot be safely applied in the regions where they are most needed, i.e. outside water intakes. In the result, additional resources are needed to periodically remove zebra mussels from entrances of water intakes and protective grids.